1. Field of the Invention
The present invention relates to an organic device, an organic electroluminescent device (hereinafter, abbreviated as an “organic EL device”) and an organic solar cell each using an organic charge-transporting compound.
2. Background Art
In recent years, organic semiconductors and organic conductive materials have been actively studied, and in particular, remarkable process has been achieved in organic EL devices which are light emissive elements that use an organic semiconductor.
In organic EL devices, Tang et al. have successfully discovered, with regard to the increase in efficiency of EL devices, that high luminance and high efficiency sufficient for practical use such as a luminance of 1,000 cd/m2 and external quantum efficiency of 1% at an applied DC voltage of not more than 10V can be obtained if a laminate structure of organic compounds having different carrier transporting properties (organic hole-transporting compounds and organic electron-transporting compounds) are applied to EL devices so that a balanced injection of holes and electrons from an anode and a cathode, respectively, is attained, and also a thickness of the organic layer sandwiched between the cathode and the anode is controlled to not more than 2,000 Å (cf. Tang et al., Appl. Phys. Lett., Vol. 51, p913 (1987); Japanese Laid-open Patent Application Nos. 59-194393, 63-264692 and 2-15595; and U.S. Pat. Nos. 4,539,507, 4,769,292 and 4,885,211).
Tang et al., also in an organic solar cell, achieved a power conversion efficiency of about 1% by laminating organic compounds having different carrier transporting properties (CuPc which is an organic hole-transporting compound and PV which is an organic electron-transporting compound) (Appl. Phys. Lett., 48, 183 (1986)).
More recently, new ideas for increasing the efficiency of aforementioned organic devices by stacking two or more units (i.e., by connecting the units in series), each of which units corresponds to the portion having been sandwiched by electrodes in prior art technology, have been published in various papers and patent publications (cf. Appl. Phys. Lett., Vol. 80, 1667 (2002), Chemistry Letters., pp. 327-330, Japanese Laid-open Patent Application No. 11-329748; U.S. Pat. No. 6,337,492; and Japanese Laid-open Patent Application Nos. 2003-45676 and 2003-264085).
In particular, the inventors of the present invention have disclosed a method of connecting two or more organic light emissive units using an electrically insulating charge generation layer (CGL) having a resistivity (specific resistance) of not less than 102 Ωcm in Japanese Laid-open Patent Application No. 2003-272860, and named the resulting device an “organic MPE (Multi-Photon Emission) EL device”. The MPE devices have been discussed and exhibited in various conferences and exhibitions so far, and obtained high appraisal (cf. 49th lecture meeting, Associate of Society of Applied Physics and others, Preprint 27p-YL-3, p. 1308; 63rd lecture meeting, Society of Applied Physics, preprint 27a-ZL-12, p. 1165; Proceedings of EL2002 (International Conference on the Science and Technology of Emissive Device and Lighting), p. 539; Proceedings of IDMC'03 (International Display Manufacturing Conference), Fr-21-01, p. 413; SID03 DIGEST, Vol. XXXIV, BOOKII, p. 964; SID03 DIGEST, Vol. XXXIV, BOOKII, p. 979; 13th lecture meeting, Production Technology Exhibition of Flat Panel Display, D-4 (2003); exhibition and distribution materials concerning white light emission device by IMES Co., Ltd. at LCD/PDP International 2002, EExpress (Nov. 15, 2002), exhibition and distribution materials concerning white light emission device by IMES Co., Ltd. at FPD International 2003, and L. S. Liao et al., Appl. Phys. Lett., Vol. 84, p. 167 (2004)).
Said charge generation layer in the MPE device has a similar structure; such that compositions of carrier (i.e., electrons and/or holes) injection layers (contacting anode or cathode), which the inventors of the present invention have introduced and developed, are laminated in sequence. Specifically, there is provided a laminated structure having, in sequence, the layer containing radical anion state of electron accepting (i.e., electron transporting) organic molecule, which are disclosed in Japanese Laid-open Patent Application Nos. 10-270171 (U.S. Pat. No. 6,013,384), 2001-102175 (U.S. Pat. No. 6,589,673), 11-233262 (European Patent No. 0936844B1) and 2000-182774 (U.S. Pat. No. 6,396,209), and the layer containing radical cation state of hole transporting organic molecule resulting from being oxidized by a strong electron accepting compound, for example, an inorganic compound such as FeCl3 and V2O5 or an organic compound such as F4-TCNQ (tetrafluoro-tetracyanoquinodimethane) and PNB (tris-β-(pentafluoronaphthyl)borane), which are disclosed in Japanese Laid-open Patent Application Nos. 11-251067 (U.S. Pat. No. 6,423,429), 2001-244079 (U.S. Pat. No. 6,589,673) and 2003-272860 and Japanese Patent Application No. 2003-358402.
Said laminated charge generation layer (CGL) composed of a layer including radical anions and a layer including radical cations can be termed “a hole current-electron current conversion layer”. In particular, among the several candidates for the laminated structure possible to achieve that conversion, the method disclosed in Japanese Patent Application No. 2003-380338 by the inventors of the present invention was found to be ideal for the serial connection of the multiple organic EL devices. For the energy barrier for electron transfer within that conversion layer (i.e., CGL) is diminished when the method is employed.
Furthermore, among the above-described technology concerning the layer including radical cation state molecules, a layer including a charge transfer complex produced upon an oxidation-reduction reaction between V2O5 and an organic hole-transporting compound (contacting each other by laminating or mixing these two compounds), was found to be most useful with respect to chemical and/or thermal stability.
However, V2O5 is categorized as a deleterious substance, and further, does not have a sufficient light transmissivity. So, the inventors of the present invention have now found that MoO3 (molybdenum trioxide) is notably superior to V2O5 with regard to the safety and the light transmissivity. Note that use of MoO3 as a constituent of an organic EL device is described in the following references, for example:
Japanese Laid-open Patent Application No. 11-67459 (Reference 1), Japanese Laid-open Patent Application No. 11-61398 (Reference 2), Japanese Laid-open Patent Application No. 2000-235893 (Reference 3), Japanese Laid-open Patent Application No. 2000-306681 (Reference 4), Japanese Laid-open Patent Application No. 2000-223276 (Reference 5), Japanese Laid-open Patent Application No. 10-199681 (Reference 6), Japanese Patent No. 2824411 (Reference 7), and S. Tokito, K. Noda and Y. Taga, J. Phys. D: Appl. Phys. 29 (11) 2750-2753, November 1996 (Reference 8).
Among the references listed above, the technology described in Japanese Patent No. 2824411, i.e., Reference 7, is also described in Reference 8 which is the technical article.
Reference 7 teaches the deposition of a metal oxide such as vanadium oxide (VOx), ruthenium oxide (RuOx) and molybdenum oxide (MoOx) at a thickness of 50 to 300 Å on ITO anode by sputtering method in order to reduce an energy barrier for hole injection from ITO anode to an organic layer, thereby providing an organic EL device capable of being operated at a lower voltage in comparison with the prior art EL devices.
However, according to the Reference 7, a layer of molybdenum oxide has only a transmittance of 10% at a thickness of 2,150 Å, and thus its thickness is limited due to the reduced light transmissivity which is considered to be resulting from oxygen desorption during the sputtering process.
Moreover, Japanese Laid-open Patent Application No. 2000-223276 describes the use of a mixture of metal oxides having the composition of indium oxide/zinc oxide/molybdenum oxide (ratio=0.65/0.25/0.1) as a hole injection layer, in order to solve the drawback of the low transparency seen in the Japanese Patent No. 2824411. Stated otherwise, in Japanese Laid-open Patent Application No. 2000-223276, they addressed this drawback (with recognizing the opacity of that sputtered molybdenum oxide layer) to satisfy both of transparency and hole injection property requirements by mixing a metal oxide having a better transparency into the molybdenum oxide. Then, the hole injection layer (having the composition of indium oxide/zinc oxide/molybdenum oxide (ratio=0.65/0.25/0.1)) is also deposited by a high frequency (i.e., RF=radio frequency) magnetron sputtering method. Similar manners are also described in Japanese Laid-open Patent Application Nos. 11-67459 and 11-61398.